Stringify properties before filtering arrays

[ianks]

Previously, filtering code allowed would blindly pass the property when calling #[] on the target input. While this usually works, it falls apart with non-string keys and can lead to some strange behaviors:

template = Liquid::Template.parse("{{ input | where: property, 0 }}")
template.render({ "input" => [5, 10, 15, 20], "property" => 1 }) # => "520"
template.render({ "input" => [5, 10, 15, 20], "property" => 0 }) # => "1020"

Let's just always coerce properties to strings, first.

[karreiro]

Thank you for this PR, @ianks!

We have a minor issue in this scenario:

{% assign fruits = 'banana apple tomato' | split: ' ' %}
{{ fruits | where: '' }}

With that fixed, I believe we're going to be ready to merge :)

[jg-rp]

it falls apart with non-string keys and can lead to some strange behaviors

It took me a while to figure out what was going on there, and I'd been struggling to explain this example too.

require 'liquid'

source = <<LIQUID
{{ some_array | find: 3 }}
{{ some_array | find_index: 1 }}
LIQUID

template = Liquid::Template.parse(source, error_mode: :lax)
puts template.render!("some_array" => [-1, 42, 1, 2, 3, 4])

I had no idea that Integer#[] was a bit access method. 😃

[ianks]

Verified this change against shadowed traffic, and this change did not impact any existing Liquid. So it should be safe to change this behavior.

[karreiro]

Thank you for verifying, @ianks!